The invention relates to visible light sources and, more particularly, to visible light sources based on AlInGaN light emitting diodes using nanocluster materials.
Solid-state light sources spanning the visible wavelength spectrum with low-power consumption and long life have uses in a number of display and illumination applications. Presently, no one materials system can be used to efficiently generate light over the entire visible energy spectrum. Light emitting diode (LED) devices have been constructed using p-doped and n-doped materials, but are generally only capable of emitting color of a narrow range of wavelengths based on the semiconductor materials used in the diode. These devices typically employ either AlInGaN or AlInGaP semiconductor materials.
AlInGaN-based LEDs can be fabricated over the green, blue and ultraviolet regions, with yellow and red wavelengths possible with very low efficiencies. LEDs fabricated from AlGaInP materials emit from the red to near-green region and AlGaAs LEDs in the deep red region. Because different material systems are necessary for a full-color (RGB) display, complex electronics modules are required to precisely control the current and voltage requirements of each material. Similarly, the generation of broadband white light is also difficult.
Light emitting devices have also been made using polymeric materials as a hole transport layer between a hole injection electrode and an electron injection electrode. Such devices, such as those using poly-(p-phenylene vinylene, are also limited to emission of a narrow range of wavelengths based on the polymeric material used. To vary the color, different polymeric materials must be used, complicating the display of light of various colors.
Because LEDs typically do not emit over a broad range of wavelengths, a number of schemes have been proposed and subsequently demonstrated to enable broadband emission with an ultimate goal of achieving a high efficiency semiconductor-based white light source. AlGaInN-based LEDs emitting in the blue (450-470 nm) region of the spectrum have been integrated with yellow phosphor materials (for example, yttrium-aluminum-garnet phosphors) to produce white light and these LEDs are available commercially. Generally speaking, these white LEDs have poor color characteristics due to having merely two color components and have color rendering index (CRI) values that can vary with injected current, temperature and angle of view. Similarly, blue LEDs have been integrated with polymer materials as well as passive AlInGaP semiconductor layers to form a two component white light source.